Locking and control circuit in a diversity telegraphy receiver



R. E. SCHOCK LOCKING AND CONTROL CIRCUIT IN A DIVERSITY TELEGRAPHYRECEIVER Jan, 31, 1950 2,495,826

Filed Sept. 18, 1946 3 Sheets-Sheet 1 l'wia-s Mam/Va 67/?60/7' 7 mam/6 VV area/r INVENTOR BY A/ ATTORNEY R. E. SCHOCK LOCKING AND CONTROLCIRCUIT IN A DIVERSITY Jan. 31, 11950 TELEGRAPHY RECEIVER Fild Sept. 18,1946 3 Sheets-Sheet 2 ATTORNEY R. E. SCHOCK LOCKING AND CONTROL CIRCUITIN A DIVERSITY Jan. 31, 1950 TELEGRAPHY RECEIVER 3 Sheets$heet 5 FiledSept. 18, 1946 um J INVENTOR brtEJciwc/f ATTORNEY Patented Jan. 31, 1950LOCKING AND CONTROL CIRCUIT IN A DIVERSITY TELEGRAPHY RECEIVER Robert E.Schock, Riverhead, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application September 18, 1946, Serial No.697,669

2 Claims.

siderable extent in connection with pulse systems Where they are drivenby pulses of one form or another fed to the trigger circuit through oneor more condensers. When it is desired to use a trigger circuit forsomething other than the transfer of or the shaping of pulses, it may bedesirable to drive said circuit from What may be called a slow varyingdirect current potential. In such a case, a problem is presented infinding a satisfactory method of applying the varying direct currentpotential to th locking circuit without destroying its triggering orlooking properties.

It is an object of the present invention to improve unidirectionalpotential drivers gering or looking circuits.

This object is attained in accordance with my invention by the use of acontrol or driver tube, the anode circuit of which includes a resistor,also included in the anode circuit of one of the locking circuit tubes.The driver tube is controlled by the unidirectional potential and thecondition of stability of the trigger or looking circuit is controlledby the magnitude of potential drop in the common resistor.

Since the locking circuit is by necessity'controlled by a driver tubeconnected therewith, the driver tube per se unbalances the triggercircuit to a certain extent to cause its switching action to benon-symmetrical or unbalanced.

A further object of my invention is to provide means for compensating orcorrecting this unbalanced condition. This object is attained byprovision of a second tube connected to the other locking circuit tubesubstantially in the same manner in which the driving tube is connectedto the first locking circuit tube. The compensating tube is then held ata selected bias so that complete balance is attained when a selectedunidirectional control potential is applied to the driving tube.

In a modification of my invention as described above, two driver tubesare used, one connected with each locking circuit tube so that thedriver tubes balance each other in the locking circuit.

Differential unidirectional potentials are then for trig- CJI 2 used ina novel manner to control the driver tubes which in turn control thecondition of stability of the locking circuit.

As indicated above, the improvements disclosed herein are of Wideapplication in the signaling art and use thereof is so intended.However, a particular use I find for the same, is in control of gatingtubes in diversity receiver systems, such as for example, frequencyshift or on-off" diversity telegraph systems, disclosed, for example, inShock et al. U. S. application Serial #632,978, filed December 5, 1945.

In diversity systems of the type disclosed in said Shock et a1.application, space or propagation intercepting diversity effects areused to obtain several versions of the same signal. These versions arethen compared as to quality so that the best signal may be selected forrecording purposes.

A further object of my invention is to provid improved means forsensingwhich signal is best and improved means for controlling a lockingcircuit by a potential derived from the signal strength sensing means.

In a modification of the means described hereinbefore, differentialcontrol potentials are to be applied to the balanced driving tubes forthe locking circuits and .a further object of my invention is to providean improved signal sensing means for deriving differentially varyingcontrol potentials which positively flip the locking circuit to acondition of stability at which it is-to be when a certain one of thesignal versions is of the greatest magnitude. It will be noted that whendifferential potentials areused for controlling the trigger circuit, amore positive action is obtained. i

In describing my invention, reference will be made to the attacheddrawings wherein: I

Figs. 1a and 11) each illustrate one embodiment of my improved triggeror looking circuit. and improved control means therefor;

Figs. 2 and 3 illustrate novel signal strength sensing means and lockingcircuit driving tube control means for the locking circuits illustratedin Figs. 1a and lb respectively.

In Fig. 1a, tubes 13 and M are the locking circuit tubes. The anodes ofthese tubes are connected by resistors H and H to the positive terminalof a direct current source, the negative terminal of which is grounded,being thereby connected through common cathode resistor K tothe'cathodes of tubes I3 and I4. The anodes and control grids of tubesI3 and M are cross coupled by resistors I! and Hi. The grid directcurrent biasing circuits for the tubes l3 and II are completed byresistors R and R. This locking circuit as described hereinbeforeoperates as follows:

Assume that current is caused to start flowing in tube [3. The potentialdrop in the re sistor ll increases to apply a less positive or morenegative potential by resistor I! to the control grid of tube M toreduce current flow in tube l4. When current flow decreases in tube I4,the potential drop in anode resistor 12 becomes less so that resistor [9applies a more positive potential to the control grid of l3 to increasecurrent flow in tube l3. The action is cumulative and carried to a pointat which tube l3 draws full current and tube I4 is cut off. The lockingcircuits stay in this position until for some reason, current flow isincreased in tube M or reduced in tube l3 to start a new tripping actionwh ch switches the current through l4 and cuts oil current flow in tubel3.

The driver tube 9 has its anode connected to the direct current sourceby the resistor H and has its cathode connected directly to the cathodeof a balancing tube l0. Both cathodes are connected to ground by acommon resistor 45. The direct current control potential is applied tothe grid I of tube 9 and for the sake of simplicity, this potential isshown as being derived from a potentiometer resistor PR; a point wh ch abe moved 1m and down to vary the potential on the grid 1. The triggerdriver tube 9 drives the trigger circuit. The balancin tube In is of thesame type as tube 9 and operates to eii'ect a balanced trigger circuitwhen the grid 1 of tube 9 has zero potential or volts applied thereto.The driver tube 9 is able to actuate the tri ger circuit because itsplate is connected to the plate 01' the trigger circuit 13. and to thesource through the common plate resistor II. The compensating or balncin tube In draws current through a resistor I 2 hich is also in theplate circuit of the tube H.

In oper tion. if trigger tube I3 is cut oil and trig er tube [4 isconduct ng. this status may be reversed by a ying posit ve potential tothe gr d of tube 9. This causes tube 9 to draw more current throughresistor II and drop the voltage I on the d of tu e [4, by wav of thecross couplro 'rnsistor to a oint w ere tube i4 is out off an the crcuit fl s to the reversed status with tube l3 conducting. Actually tubeI0 aids somewhat in dri ng the trigger to reverse because the pos tivepotential applied to tube .9 .not on y increases the p ate current flowthrough resistor H. but also the cathode current flow throu 'h r si tor5. S nce this resistor is common to both tubes 9 and H], the increasedpos tive p tential across this cathode resistor tend to bias tube In todraw less current. This decrease n current through resistor 12 increasesi frequency shift diversity system is illustrated in Fig. 2. In thisdiversity system, it is assumed that there are two receivers, one ofwhich is designated receiver A and the other of which is designatedreceiver B. These receivers are excited by spaced antenna systems fordiversity efiects and may comprise radio frequency amplifiers, frequencychangers or converters including a detector and local oscillator and anintermediate frequency amplifier supplying output to terminals 3D and30. The intermediate frequency output which is shifted in frequency inaccordance with signals is supplied by coupling condensers 32 and 32' tothe third grid electrodes in gating tubes 34 and 34. The gating tubesoperate as disclosed in Schock et a1. application, Serial #632,978,filed December 5, 1945, to suppiy output from one receiver or the otherto a common load ZL for use as described in said application. The gatingtubes are controlled by the trigger circuit. The trigger circuit per seis as illustrated in Fig. 1a and the description thereof will not berepeated here. It will be noted that the potentials at the points X andX vary differentially as the trigger circuit is tripped between its twostates of stability and that these potentials at X and X vary from sayabout zero potential to some negative value sufliciently high to cut oifthe tubes 34 and 34' controlled thereby. The points X and X are coupledby resistors 38 and 38' to controlling electrodes in the gate tubes 34and 34' to differentially control the operation of the gating tubes asdescribed above.

Receiver A and recei er B o t ts are cornpared as to strength in asignal strength sensing means designated generally at 50. This meanscomprises transformers T and T' having band pass characteristicssufficiently wide to pass without material attenuation all of thefrequency components in a frequency shift signal of intermediatefrequency such as supplied at the output of receivers A and B. Thesetransformers T and "I" each have secondary windings connected in aseparate rectifier circuit including in series with the secondarywinding of transformer T a rectifier diode .54, a load resistor 58 and abypass condenser 51. The secondary winding of transformer T is similarlyconnected in a rectifier circuit, elements of which are designated bynumerals or letters corresponding to the numerals or letters used in thepreceding sentence adding prime. It will be noted that the rectifierload resistors 56 and 56' are so connected that the potential dropsproduced therein o pose. Thus, when the signals are of like strength,the potential at the point P should be and is substantiall zero. In thisrespect, note that the cathode of the rectifier 54' is grounded. Thispotential at P will become positive when the signal at receiver A isstronger than the signal at receiver B and will become negative when thesignal at receiver A is weaker than the signal at receiver B. This willbe apparent by an inspection oi. the polarities in which the rectifiersare connected to the load impedances. The'potentied at P then varies iwith respect to zero potential and is supplied to the control grid 1 ofthe driver tube 9. If we assume that this potential swings negativewhich it would if the signal in receiver A is the weakest, the tube 9would become less conductive to draw less current through resistor I andthe anode potential of tube J3 would rise or become more positive aswould the grid potential of tube I4. This would 75 operate as describedhereinbefore to switch the current through tube 14 and make thepotential at the point X more positive. This potential is applied by theresistor 38 to the controlling grid of the gate tube 34' to make thistube operative to supply signal to the load ZL and this signal issupplied from receiver B wherein the signal is the strongest. When thepotential at the point P becomes positive. a second tripping actiontakes place as described before to switch, the current through the tubel3 to make more positive the potential at the point X and more negativethe potential at the point X, to make tube 34 operative. to pass signalfrom receiver A and to cut ofi tube 34' to block signal from receiver B.

.The voltage peak limiting tubes 69 and. 69 and their purpose andoperation in the triggering circuit have been described in Schock et a1.application. Serial #630429, filed November 23,

1945. now abandoned, and the description thereof will not be repeatedherein.

The novel compensated tri gering circuit of Fig. 1b is used in thediversity receiver system of Fig. 3. The arrangement here is asdescribed hereinbefore in connection with Fig. 1b and Fig. 2 except forthe following diflerences:

The signal sensing circuit is now to provide differentially actingcontrol potentials. one for the grid I of the driver tube 9 and theother for the grid 8 of the driver tube Ill. The signal strength sensingor comparing circuit designated generally at 50, now comprises.connected. with the secondary of transformer T, diodes 54 and 55arranged in op osed polarity with rectifier loads 59 and GI. Thesecondary of transformer T is similarly connected in rectifier circuitsincluding rectifier tubes 54' and 55' similarly connected in o posedpolarity with load 59' and load 6|. The load 59 is connected in a seriescircuit including said load. the potential (combiner) divider incl dingresistors 19 and 12 and the rectifier load 59'. The rectifier load BI isin a series circuit with the potential (combiner) div der comprisingresistors 14 and 16 and the rectifier load 6|. It will be further notedthat the diodes 55 and 55' are of opposed polarity and are excited by asignal from each receiver. Their loads 59 and 59' are in series with thepotential (combiner) divider including resistors 19 and 12 to provide atpoint P a potential which varies above say zero potential in a negativedirection when the signal at the receiver A is the weakest. Thispotential is applied to the grid of driver tube 9. The rectifiers 54 and54' likewise excited by energy from receivers A and B respec ively, areof opposed polarity with loads 6| and 6| in a series circuit grounded ata point between loads GI and 6! which series circuit includes resistors14 and 16 adjacent terminals of which at point P are connected to thecontrol grid 8 of tube ID. This rectifier arrangement is such that whenthe signal at the receiver A is the strongest, the potential at point Pbecomes more positive and the potential at point P less positive or morenegative. Then the potential on the grid 8 of tube l becomes morenegative to assist in switching current through tube l3 to make thepotential at point X more positive and the potential at point X morenegative to cut-off gating tube 34' and turn on gating tube 34 to passthe signal supplied by receiver A. When the signal from the output ofreceiver A is weaker than the signal from the output of receiver B, thepotential at the point P becomes more negative while the potential atthe point P becomes more positive to cut of!" current in the tube 13 andpass full current through the tube M to make more positive the potentialat the point X to turn on tube 34' and turn off tube 34.

Normally in Fig. 3, the two transformers T and T would be identical andso would all of the diode load resistors 59, 6|, 59' and BI. Normallyalso resistors 10 and 12 would be identical to each other in value andmay be equal to or severaltimes greater in value than the loadresistors. The same may be said of resistors 14 and 16. Perhaps I maybest explain the function of resistors 10 and 12 by referring to Fig.1a. In Fig. 3 the center tapped battery of Fig. 1a may be said to havebeen replaced by the diode load resistors 59 and 59'. Now in Fig. 1a thetwo halves of the battery gave an unvarying potential supply so thepotentiometer PR was used to supply voltage variations to the grid oftube 9. But in Fig. 3, where the center tapped battery is replaced byload resistors 59 and 59, there are varying potentials across these loadresistors, the differential of which is applied to the grid of tube 9.So the potentiometer of Fig. 1a becomes a fixed divider in Fig. 3embodying resistors 10 and 12 of equal value; The value of theseresistors is kept high with respect to the load resistors 59 and 59 inorder not to shunt these load resistors down unnecessarily.

What is claimed is:

1. In means for comparing the relative strengths of two currents whichare representative of diversified versions of the same signal and forderiving potentials which vary differentially when the relativestrengths of said currents vary, a first pair of rectifier systemsincluding an alternating current path having a common portion excited byone of said currents and two direct current branch portions eachincluding a load impedance and a rectifier device with the devices inopposed relation so that the potential drops across said loads are ofopposed polarity, a second pair of rectifier systems having analternating current path including a common portion excited by the otherof said currents and two direct current branch portions each including aload impedance and a rectifier device with the last mentioned devices inopposed relation so that the potential drops across said last two loadimpedances are of opposed polarity, a connection between adjacentterminals of said first-mentioned load impedances and adjacent terminalsof said second-mentioned load impedances, a circuit including adjacentseries output impedances for adding in series the potential drops acrossa load impedance of said first-mentioned two load impedances and a loadimpedance of said secondmentioned two load impedances, a second circuitincluding adjacent series output impedances for adding in series thepotential drops across the remaining load impedances, and means forderiving said differentially varying potentials from adjacent terminalsof said output impedances.

7 of said source and the other output electrodes of the flow devices,means cross coupling the positive output electrodes and controlelectrodes of the flow devices so that when current starts to flow inone device, it is cut off in the other device and vice versa, a pair ofcontrol devices each having a positive output electrode coupled to thepositive output electrode of a diflerent one of said locking circuitdevices and each having another output electrode with a common resistorcoupling the last-named output electrodes to the negative terminal ofsaid source, each of said control devices having a control electrode,and means for applying control potentials differentially to said controldevice control electrodes including a first full wave rectifier circuitincluding series load impedances excited by signals from both of-saidreceivers, a connection between said load impedances and the controlelectrode of one control device, a second full wave rectifier circuitincluding series load impedances excited by signals from both of saidreceivers, and a connection between theload .impedances .ofsaidsecondrectiiler cirrcuit and the control electrode-oi the other.controldevican ROBERT. E. SCHOCK. 1

I REFERENCES CITED The following references are of record in the file ofthis patent: V

" UNITED' STATES PA Hollingsworth Dec. 30,

